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Make contravariant inferences only from pure contravariant positions #27357

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Merged
merged 4 commits into from
Sep 26, 2018
Merged

Make contravariant inferences only from pure contravariant positions #27357

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5e55118
Only make contravariant inferences from pure contravariant positions
ahejlsberg Sep 26, 2018
4bb5cfb
Add regression test
ahejlsberg Sep 26, 2018
2721571
Accept new baselines
ahejlsberg Sep 26, 2018
f59229b
Only add unique inferences to candidate arrays
ahejlsberg Sep 26, 2018
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14 changes: 11 additions & 3 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -13460,6 +13460,7 @@ namespace ts {
let symbolStack: Symbol[];
let visited: Map<boolean>;
let contravariant = false;
let bivariant = false;
let propagationType: Type;
let allowComplexConstraintInference = true;
inferFromTypes(originalSource, originalTarget);
Expand Down Expand Up @@ -13546,11 +13547,13 @@ namespace ts {
}
if (priority === inference.priority) {
const candidate = propagationType || source;
if (contravariant) {
inference.contraCandidates = append(inference.contraCandidates, candidate);
// We make contravariant inferences only if we are in a pure contravariant position,
// i.e. only if we have not descended into a bivariant position.
if (contravariant && !bivariant) {
inference.contraCandidates = appendIfUnique(inference.contraCandidates, candidate);
}
else {
inference.candidates = append(inference.candidates, candidate);
inference.candidates = appendIfUnique(inference.candidates, candidate);
}
}
if (!(priority & InferencePriority.ReturnType) && target.flags & TypeFlags.TypeParameter && !isTypeParameterAtTopLevel(originalTarget, <TypeParameter>target)) {
Expand Down Expand Up @@ -13798,7 +13801,12 @@ namespace ts {

function inferFromSignature(source: Signature, target: Signature, skipParameters: boolean) {
if (!skipParameters) {
const saveBivariant = bivariant;
const kind = target.declaration ? target.declaration.kind : SyntaxKind.Unknown;
// Once we descend into a bivariant signature we remain bivariant for all nested inferences
bivariant = bivariant || kind === SyntaxKind.MethodDeclaration || kind === SyntaxKind.MethodSignature || kind === SyntaxKind.Constructor;
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Doesn't this only need to be set on the specifically contravariant comparison within forEachMatchingParameterType? Also, could we not use a single variance variable for both bivariant and contravariant context tracking (seeing as we have a variance enum already)?

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The contravariant flag continues to track whether the position is co- or contra-variant, regardless of whether we've descended into a bivariant position. Doing it this way, using two separate boolean variables, makes the logic that flips the flag easy. I looked at keeping it in a single variable but didn't like the complexity that came with it.

forEachMatchingParameterType(source, target, inferFromContravariantTypes);
bivariant = saveBivariant;
}
const sourceTypePredicate = getTypePredicateOfSignature(source);
const targetTypePredicate = getTypePredicateOfSignature(target);
Expand Down
17 changes: 17 additions & 0 deletions tests/baselines/reference/bivariantInferences.js
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@@ -0,0 +1,17 @@
//// [bivariantInferences.ts]
// Repro from #27337

interface Array<T> {
equalsShallow<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>): boolean;
}

declare const a: (string | number)[] | null[] | undefined[] | {}[];
declare const b: (string | number)[] | null[] | undefined[] | {}[];

let x = a.equalsShallow(b);


//// [bivariantInferences.js]
"use strict";
// Repro from #27337
var x = a.equalsShallow(b);
31 changes: 31 additions & 0 deletions tests/baselines/reference/bivariantInferences.symbols
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@@ -0,0 +1,31 @@
=== tests/cases/conformance/types/typeRelationships/typeInference/bivariantInferences.ts ===
// Repro from #27337

interface Array<T> {
>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(bivariantInferences.ts, 0, 0))
>T : Symbol(T, Decl(lib.es5.d.ts, --, --), Decl(bivariantInferences.ts, 2, 16))

equalsShallow<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>): boolean;
>equalsShallow : Symbol(Array.equalsShallow, Decl(bivariantInferences.ts, 2, 20))
>T : Symbol(T, Decl(bivariantInferences.ts, 3, 18))
>this : Symbol(this, Decl(bivariantInferences.ts, 3, 21))
>ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --))
>T : Symbol(T, Decl(bivariantInferences.ts, 3, 18))
>other : Symbol(other, Decl(bivariantInferences.ts, 3, 44))
>ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --))
>T : Symbol(T, Decl(bivariantInferences.ts, 3, 18))
}

declare const a: (string | number)[] | null[] | undefined[] | {}[];
>a : Symbol(a, Decl(bivariantInferences.ts, 6, 13))

declare const b: (string | number)[] | null[] | undefined[] | {}[];
>b : Symbol(b, Decl(bivariantInferences.ts, 7, 13))

let x = a.equalsShallow(b);
>x : Symbol(x, Decl(bivariantInferences.ts, 9, 3))
>a.equalsShallow : Symbol(equalsShallow, Decl(bivariantInferences.ts, 2, 20), Decl(bivariantInferences.ts, 2, 20), Decl(bivariantInferences.ts, 2, 20), Decl(bivariantInferences.ts, 2, 20))
>a : Symbol(a, Decl(bivariantInferences.ts, 6, 13))
>equalsShallow : Symbol(equalsShallow, Decl(bivariantInferences.ts, 2, 20), Decl(bivariantInferences.ts, 2, 20), Decl(bivariantInferences.ts, 2, 20), Decl(bivariantInferences.ts, 2, 20))
>b : Symbol(b, Decl(bivariantInferences.ts, 7, 13))

26 changes: 26 additions & 0 deletions tests/baselines/reference/bivariantInferences.types
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@@ -0,0 +1,26 @@
=== tests/cases/conformance/types/typeRelationships/typeInference/bivariantInferences.ts ===
// Repro from #27337

interface Array<T> {
equalsShallow<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>): boolean;
>equalsShallow : <T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>) => boolean
>this : ReadonlyArray<T>
>other : ReadonlyArray<T>
}

declare const a: (string | number)[] | null[] | undefined[] | {}[];
>a : (string | number)[] | null[] | undefined[] | {}[]
>null : null

declare const b: (string | number)[] | null[] | undefined[] | {}[];
>b : (string | number)[] | null[] | undefined[] | {}[]
>null : null

let x = a.equalsShallow(b);
>x : boolean
>a.equalsShallow(b) : boolean
>a.equalsShallow : (<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>) => boolean) | (<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>) => boolean) | (<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>) => boolean) | (<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>) => boolean)
>a : (string | number)[] | null[] | undefined[] | {}[]
>equalsShallow : (<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>) => boolean) | (<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>) => boolean) | (<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>) => boolean) | (<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>) => boolean)
>b : (string | number)[] | null[] | undefined[] | {}[]

12 changes: 12 additions & 0 deletions tests/cases/conformance/types/typeRelationships/typeInference/bivariantInferences.ts
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@@ -0,0 +1,12 @@
// @strict: true

// Repro from #27337

interface Array<T> {
equalsShallow<T>(this: ReadonlyArray<T>, other: ReadonlyArray<T>): boolean;
}

declare const a: (string | number)[] | null[] | undefined[] | {}[];
declare const b: (string | number)[] | null[] | undefined[] | {}[];

let x = a.equalsShallow(b);